Film formation on lithium electrode in LiAlCl[sub 4]/SO[sub 2]Cl[sub 2] and LiAlCl[sub 4]:3SO[sub 2] based electrolytes

The surface film on lithium in LiAlCl[sub 4]/SO[sub 2]Cl[sub 2] electrolyte, LiAlCl[sub 4]:3SO[sub 2] solvate, and mixture of these two electrolytes has been studied using ac impedance and scanning electron microscopy coupled to energy dispersive X-ray analysis. The film was found to be essentially LiCl in the case of LiAlCl[sub 4]/SO[sub 2]Cl[sub 2] and the mixture of LiAlCl[sub 4]:3SO[sub 2] solvate and LiAlCl[sub 4]/SO[sub 2]Cl[sub 2] electrolyte. Differences in the film morphology were observed according to the nature of the electrolyte. Electro-chemical results implied that the passivating layer behaved as a two-layer film, a primary thin and compact film and a secondary porous film which progressively covered the inner layer. The nature of the electrolyte and especially the presence of SO[sub 2] at the interface, was found to influence the growth of the film. A model of formation and growth of the passivating film is proposed to describe the behavior of the lithium in these electrolytes.